A study shows urban vegetation correlates with reduced crime rates.

One school of thought has it that inner-city trees and shrubs make convenient hiding places and covered escape routes for criminals. Another, supported by an increasing body of evidence, argues that urban foliage may actually reduce crime. Where previous studies have tended to focus on individual housing blocks or, at best, neighborhoods, new research out of Temple University is among the first to examine the issue at the city-scale. TU researchers analyzed the relationship between vegetation concentration and crime for the whole of Philadelphia.

The researchers broke the city down into 363 "tracts" identified from socioeconomic census data, each containing between 100 and 8,000 people. The data, taken from the years 2005 to 2009, was also used to assess poverty and education levels in these tracts. Vegetation coverage was assessed from satellite imagery from 2005, courtesy of NASA's Landsat 7. Recorded incidents of aggravated assault, robbery, burglary, and theft were drawn from the University of Pennsylvania's Neighborhood Information System CrimeBase, also for the year 2005.

Theft, just to be clear, is the illegal act of taking something without permission. Robbery is the same, but with violence (or the threat of it). Burglary is breaking into a building in order to a commit crime (often, but not necessarily, theft or robbery.) The researchers ignored incidents of murder and rape on the grounds that their relative rarity renders the comparison senseless at tract level.

The team undertook a series of statistical analyses of the data, including multivariate ordinary least squares regression. This allowed them to test the "explanatory power" of foliage on crime while controlling for other influences on it, like population density, poverty, and education. Other techniques allowed for the control of the spatial contagion of crime.

A visual assessment of the data confirmed a negative correlation between vegetation and crime (i.e. the more vegetation in an area, the fewer incidents of crime there tend to be), and the statistics bear this out. "Notably, vegetation is significantly and negatively correlated with all of the crime variables, with the exception of thefts," the study finds. "As vegetation increases, aggravated assaults, robberies, and burglaries decrease."

Unsurprisingly, the greenest parts of the city tend to be home to wealthy and educated people. Controlling for these other potential causes, however, the researchers found that the correlation stands. "[V]egetation has a significant and negative relationship with all three types of crime, even after accounting for poverty, educational attainment, and population density," the study finds. (Note: the three crimes excluded theft due to the lack of significant correlation to begin with.)

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By way of explanation, the researchers echo hypotheses from prior studies. There are two arguments. The first is that more vegetation promotes the use of public space, leading to more "social supervision" and surveillance. Social supervision, in essence, is the idea that people are more likely to establish beneficial relationships with positive, crime-deterring role models. Increased surveillance, meanwhile, does not imply the proliferation of CCTV. This is simply a reference to more users of a space bringing more eyes to the street. The theory: ne'er-do-wells don't like being observed when ne'er-do-welling.

The second argument is that vegetation provides a "mentally restorative effect" that can reduce violent crime. The implication is not so much that a glimpse of hydrangea will deter a violent criminal in the act, but that the presence of vegetation reduces mental fatigue and irritability, which can be the precursors to violent crime. The authors admit that such benefits are difficult to quantify, but their results would seem to support this idea. The negative correlation between vegetation and crime was stronger for incidents of robbery and aggravated assault.

Chief among the limitations of the study was the means by which vegetation was identified, the Normalized Difference Vegetation Index (NDVI). NDVI involves assessing satellite data for the quality and health of vegetation by comparing reflected light and reflected near-infrared radiation (plants absorb most of the former but little of the latter). Though the method can distinguish trees from lawns and shrubs, it cannot distinguish between specific types of vegetation, tree crown area, or the upkeep of the vegetation.

This can be a problem, as the authors suggest that overgrown abandoned lots broadcast a lack of social control that will encourage crime. Neither does the study distinguish between public and private property, which other research has found to be relevant.

There will be other contributory factors overlooked in this research, the authors point out. These may include demographic, cultural, and urban morphological factors (such as the age of a building or its proximity to a transport hub). Though nothing on this list, they suggest, prompts an obvious alternative explanation for the relationship of crime with vegetation.

The authors also point out that the study cannot rule out the possibility that vegetation is displacing crime rather than reducing it. To assess this would require monitoring changes in crime and vegetation over time. That's impossible with the data they had, but it's an avenue of future research.

This latest study adds to the mounting evidence that there is a clear negative correlation between urban vegetation and crime. What it does not do, beyond doubt, is prove causation. Though the team has attempted to control for other causal factors, there remains the distinct possibility that vegetation is a proxy and some as-yet unidentified variable is the actual cause.

Nevertheless, this is an area of research city planners and police departments would do well to monitor. Vegetation is sometimes removed in efforts to curb crime. It may yet prove that the opposite policy is more effective.

I was going to comment about causation not being clear, but then I saw that the article already says as much down near the end. One could imagine all kinds of causes in the other direction - the kinds of neighborhoods that get more vegetation already being less crime prone, for example, just because maybe having more vegetation tends to indicate that someone cares at least a little.

i'm not sure i read it right, but it sounded like they measured the amount of shrubbery in total, whether public or private, and then made a correlation to the amount of crime and started talking about the impact of shrubbery in public places specifically. i'm left wondering if private-land shrubbery is more impactful; a possible hypothesis being that citizens who tend to their gardens also tend to their streets.

Correlation does not equal causation. I'd wager that the shrubbery is generally present in nicer neighborhoods with higher median household incomes, education and lower unemployment.

I would be rather surprised if putting in some trees and urban greenery in poorer areas of Philadephia (or other blighted areas like west Chicago) would somehow reduce crime. If you want to reduce crime, look at places which have very low crime and do what they did. Poverty and crime go hand in hand, and if you are willing to accept areas of extreme poverty in your society, then you better be ready to accept the crime as well.

Unsurprisingly, the greenest parts of the city tend to be home to wealthy and educated people. Controlling for these other potential causes, however, the researchers found that the correlation stands. "[V]egetation has a significant and negative relationship with all three types of crime, even after accounting for poverty, educational attainment, and population density," the study finds. (Note: the three crimes excluded theft due to the lack of significant correlation to begin with.)

In other words, they did a multivariate analysis and isolated other influences. How well they did this would be something you might be able to argue on, but beyond that your post seems to have completely missed this aspect of the study, which is what actually makes it interesting beyond just a "well hur de dur."

Dunno why everyone seems to be so dead-set on bashing this study. It took some simple data and found fairly strong correlations. From what it sounds like the authors would like to use this to make more in-depth studies that might be able to find stronger correlation (e.g. better vegetation data) and/or causation (vegetation over time.)

I really like studies like this. They present new ideas for actual issues, and offer the steps needed to figure out if it truly is a viable solution.

I'd like to know what degree of significance is the correlation. A slight R could be masking quite a few other variables, as mentioned in the article, whereas a strong correlation would be more useful in drawing conclusions.

I think it would still be a good idea to include more greenery and life to the city even if it doesn't obviously diminish crime. The vegetation (like parks for instance) might prompt people to be more active and involved in the outdoors which itself can deter crime.

I think it would make more sense to measure the correlation between line-of-sight to a park or vegetation, and correlation between access to a park or vegetation. If you can see green out your window, would you be more/less likely to commit theft/robbery/burglary?

can you develop a crime coefficient based on #of blocks to a park or dense vegetation?

I think the division of "tracts" should be based on vegetation and not on census - socio-economic data. Then you can correlate the effects of vegetation. this study seems backwards.

In Europe, the distribution of wealth in cities is almost the opposite of the USA. In Sweden, we never had a mass-exodus from the inner cities to wealthier suburbs like in the USA. Our suburbs were mostly apartment complexes built on cheap land for the working class and those moving in to the cities from the countryside looking for jobs. Nowadays, those areas house the majority of newly arrived immigrants that come to the country.Those who could afford it renovated their inner city apartments and stayed in the cities despite the lack of vegetation. Prices for apartments in larger cities are now out of reach for most working people.

However, those suburban apartment complexes were often built on greenfield land or within actual forests, meaning the surroundings are very green and full of shrubbery. Still, they are the areas with the highest crime rates etc. (not counting some of the busiest inner-city streets were all the night clubs etc. are).So I don't think the presence of vegetation itself deters crime. However, I think quality public spaces (parks, market squares etc., but not random bits of nature that were just left) encourage people to be more social and approachable, which deters crime.

I think it would make more sense to measure the correlation between line-of-sight to a park or vegetation, and correlation between access to a park or vegetation. If you can see green out your window, would you be more/less likely to commit theft/robbery/burglary?

can you develop a crime coefficient based on #of blocks to a park or dense vegetation?

I think the division of "tracts" should be based on vegetation and not on census - socio-economic data. Then you can correlate the effects of vegetation. this study seems backwards.

encourage people to be more social and approachable, which deters crime.

I think every robbery begins with an approach.

--Well, I wonder what this has to do with the Space Station. Yeap, NASA found that astronauts stress levels drop when the are around vegetation. Maybe we have the same effect in the concrete (rather than aluminum) jungle?

Still, they are the areas with the highest crime rates etc. (not counting some of the busiest inner-city streets were all the night clubs etc. are).So I don't think the presence of vegetation itself deters crime.

Evidently one major difference is that most of the greenery in the U.S. suburbs is private ownership, whereas most –or all– of the greenery in European banlieues is State-owned.

Hence it would make sense that most European suburbs would be dirty and dangerous (with exceptions of course such as über-wealthy Neuilly-sur-Seine being the exception that proves the rule).

Would it be too much effort to tell us the value of this negative correlation coefficient? There are no numbers in the article which show how strong the relationship was. As the referenced publication is paywalled at a cost of $40, there isn't any way for the majority of us to read it.

Not to get on a big rant about it, but it always reeks of bad science reporting when these details are neglected. "A new study confirms that broccoli reduces the risk of certain types of cancer" .... by how much? A reduction of a few percent should not be enough to convince anyone to go on a broccoli binge for the rest of their lives.

The word 'significant' is also used in a misleading way in the article. I suspect the author is referring to the broad concept of 'statistical significance', as eluded to in the article abstract. Yet no one even mentions the specifics of the hypothesis test or what significance level it was evaluated at. 'Significant' in the statistical sense is a very malleable term whose implications can be widely different than what a regular person would consider significant.

However, I think quality public spaces (parks, market squares etc., but not random bits of nature that were just left) encourage people to be more social and approachable, which deters crime.

This may be the crux of it right here...

Paradoxically, highly urbanized areas can often give a greater sense of anonymity than smaller communities. There can be thousands of people, but the vast majority are strangers, with no connection to one another, besides physical proximity. For those of our brethren leaning toward bad behavior, not having strong social connections to their surroundings probably increases the likelihood of lawbreaking.

Correlation does not equal causation. I'd wager that the shrubbery is generally present in nicer neighborhoods with higher median household incomes, education and lower unemployment.

I would be rather surprised if putting in some trees and urban greenery in poorer areas of Philadephia (or other blighted areas like west Chicago) would somehow reduce crime. If you want to reduce crime, look at places which have very low crime and do what they did. Poverty and crime go hand in hand, and if you are willing to accept areas of extreme poverty in your society, then you better be ready to accept the crime as well.

Still, they are the areas with the highest crime rates etc. (not counting some of the busiest inner-city streets were all the night clubs etc. are).So I don't think the presence of vegetation itself deters crime.

Evidently one major difference is that most of the greenery in the U.S. suburbs is private ownership, whereas most –or all– of the greenery in European banlieues is State-owned.

Hence it would make sense that most European suburbs would be dirty and dangerous (with exceptions of course such as über-wealthy Neuilly-sur-Seine being the exception that proves the rule).

Hmm...That would depend on locality. In the DC area, there is plenty of public open space in all of the surrounding suburbs. Not to mention that many neighborhoods in the city have large amounts of green space on private parcels.

"What it does not do, beyond doubt, is prove causation. Though the team has attempted to control for other causal factors, there remains the distinct possibility that vegetation is a proxy and some as-yet unidentified variable is the actual cause."

My first thought was that an increase in foliage means a decrease in "used" land and an increase in preventive features: Using land only for visual landscaping purposes and not exploiting it for human structures or other purposes is relatively expensive. For instance, consider a large estate or even gated community with a lot of land and "foliage" but proportionally small percentage of human structures or other exploitation, which because of the relative wealth required to afford the luxury of that unexploited land would also tend to have much more aggressive security features. They need to rule out that and other factors in a follow-up.

Its not the fact that there is shrubbery or tree's. It is the fact that in areas where the residents actually give a crap enough to plant trees and shrubs ect the crime rate is lower. Why? Because the people living there actually give a damn about where they live.If you plant tress and shrubs in a area where the people living there just don't give a crap it wont effect the crime rate. unless you think muggers and thieves are afraid of trees.

I can't give a reference but there was an earlier controlled study somewhere (New York?), where they found even a few street trees and planter boxes in city residential areas reduced street crime by about 6%.

Buying a sapling, planting it and looking after it is pretty much the most useful, satisfying and most generous act a person can do compared to the time and cost of actually doing it. Want to make the world a better place? Plant a tree.

Its not the fact that there is shrubbery or tree's. It is the fact that in areas where the residents actually give a crap enough to plant trees and shrubs ect the crime rate is lower. Why? Because the people living there actually give a damn about where they live.If you plant tress and shrubs in a area where the people living there just don't give a crap it wont effect the crime rate. unless you think muggers and thieves are afraid of trees.

Does it astonish you that anyone bothers to collect data and do analysis of that data when they could just ask you for the 'obvious' answer?

Alternatively: how do you know that the presence of trees and shrubs, etc. correlates with residents 'give a crap enough' (for whatever definition of that phrase you care to supply)? Is this just 'obvious', or do you have your own study to point at?

Its not the fact that there is shrubbery or tree's. It is the fact that in areas where the residents actually give a crap enough to plant trees and shrubs ect the crime rate is lower. Why? Because the people living there actually give a damn about where they live.If you plant tress and shrubs in a area where the people living there just don't give a crap it wont effect the crime rate. unless you think muggers and thieves are afraid of trees.

Does it astonish you that anyone bothers to collect data and do analysis of that data when they could just ask you for the 'obvious' answer?

Alternatively: how do you know that the presence of trees and shrubs, etc. correlates with residents 'give a crap enough' (for whatever definition of that phrase you care to supply)? Is this just 'obvious', or do you have your own study to point at?

So you found the degree of correlation that so we of us were asking about earlier?

Its not the fact that there is shrubbery or tree's. It is the fact that in areas where the residents actually give a crap enough to plant trees and shrubs ect the crime rate is lower. Why? Because the people living there actually give a damn about where they live.If you plant tress and shrubs in a area where the people living there just don't give a crap it wont effect the crime rate. unless you think muggers and thieves are afraid of trees.

Does it astonish you that anyone bothers to collect data and do analysis of that data when they could just ask you for the 'obvious' answer?

Alternatively: how do you know that the presence of trees and shrubs, etc. correlates with residents 'give a crap enough' (for whatever definition of that phrase you care to supply)? Is this just 'obvious', or do you have your own study to point at?

So you found the degree of correlation that so we of us were asking about earlier?

Unfortunately for me, I no longer have access to any journal subscriptions, so no, I haven't.

What does this have to do with johnross1968's willingness to declare that the causal link between the two items is 'residents actually giv[ing] a crap'?

The truth is probably the exact reverse - nicer areas are more likely to have vegetation. I know that Oregon is a fairly nice place to live and our cities are full of vegetation, and the least nice parts of town tend to be the least vegetated and the most ugly - but its not because of the lack of vegetation, its a reflection of the kind of people who end up living in that sort of place.

This is the problem with a lot of people. Its very similar to the storks delivering babies thing - there is a statistical correlation, but having more storks in the area doesn't cause more people to have kids, its that they both happen in the same sort of place.

The first thing that comes to my mind, after actually reading the article, is how easily this study sh/could be replicated in cities at least US-wide if not taken up by international researchers. The satellite info should be available and crime stats as well.

Will it hold up here, in DC, where greenery is prevalent? What about concrete jungles like NY, chicaco, and LA? If not, it sort've kills this idea where it stands. If so, it makes the whole concept much, much more interesting.

Since the follow-up is so straightforward, I hesitate to even worry about trying to support or criticize it. Let the scientific method move forward. That should be the easiest and most straightforward test of this idea.

I don't find their second hypothesis particularly compelling. "The second argument is that vegetation provides a "mentally restorative effect" that can reduce violent crime."

Only one of the the crimes measured (aggravated assaults) is both impulsive and violent. (Robbery is all about the implied threat of violence against the victim). That doesn't give much bearing on the rates of burglary or robbery.

I was going to comment about causation not being clear, but then I saw that the article already says as much down near the end. One could imagine all kinds of causes in the other direction - the kinds of neighborhoods that get more vegetation already being less crime prone, for example, just because maybe having more vegetation tends to indicate that someone cares at least a little.

Not to mention going from more granular to less granular in the scale of the study makes all the findings suspect at best by comparison to the neighborhood area studies, or even the block area studies (which conversely may be too granular to draw real conclusions from).

As someone in the commercial plant industry I like this. There are other studies that show people are more likely to enjoy their neighborhood more with properly maintained green space and I know several shrubberies you would have to be really desperate to attempt hiding in(thorns, lots of thorns). The key part being properly maintained, if the city can't afford the maintenance (and which city can these days) then it will get out of control and probably be a negative factor. These becomes more prevalent in lower income/high density neighborhoods where the likelihood of the residents working on it is lower. Abandoned lots can be a huge problem and the more of these converted to community gardens and public green spaces the better as the article mentions it is hard to separate them from actually green spaces when overgrown. All in all it seems like a much cheaper path to urban renewal than most alternatives